Imagine a hormone in your brain would determine not only your emotional state (yay for dopamine!), but your job. You go to your doctor for the biannual check-up and get a call a few days later. Your palms start to sweat. This can only mean one thing. And it´s about to happen. “I´m sorry, the dopamine levels in your frontal cortex have peaked. In the next days, you will lose your arms and grow hammer-shaped forelimbs instead.” You take a deep breath in order to stay calm. You´re not ready for this yet. “Doc, are you sure? I don´t feel like I´m mentally prepared to be a handyman yet.” You can hear him suppressing a laugh on the other end. “Trust me, your brain is ready for this transition. You´ve never been more mentally prepared in your life!” Your brain is going into overdrive. You wanted to be a writer! An artist! Alas, you are a nurse, which is fine, but it mostly just pays for your writing career. Your new novel was about to be finished. This wasn´t time to turn into a handyman! “No, there´s got to be something you can do about this!” – “You know I can´t, society needs you as a handyman now. So, take care and try not to be lifting anything heavy over anyone´s head the moment your arms come off.” The phone clicks and beeps softly. “No!” You let yourself fall back onto your bed. A week till your life will completely change.
Seven days later. You´re still having trouble adjusting to drinking out of a glass without using your hands. You would keep straws permanently at hand – if you still had some. The work is better than expected though. The hammering and screwing seem to be things you were born to do – which, in a sense, you were. It´s even better than working on your, if you´re honest, very mediocre novel. Content and happy with yourself – it was a productive today – you are about to sit down on the couch, when the phone rings again. You ask your child – thank goodness it´s young enough to still have hands – to answer it for you and hold it to your ear. “Yes, this is me speaking, who is it?” – “Hello, it´s the Doctor again. Our statistic apartment went through the numbers. We don´t need handymen anymore, but we are lacking nurses. You know what this means.” – “You´ve got to be kidding me! I go through all of the arm – losing, hammer-growing, job – adjusting stage only for you to change your mind?! I LIKED this job! I won´t do it!” The Doctor sighs at the other end. “Society has decided. The change will happen tomorrow. “ Beep, beep, beep. You stare at your hammer-hands and shake your head. If only you could decide yourself.
The bee brain harbors the molecules that can make exactly this happen to the honeybee. Eusociality – the highest level of organization in the entire animal kingdom – doesn´t just happen. What it relies on is harmony despite inequality through neurochemistry and genetics. The most defining characteristic of a eusocial insect society and one of the things that has enabled the bee to survive 40 million years is their highly developed division of labor. What role does neurochemistry play in all this – and how?
After hatching, female bees go through very time – dependent social roles in the hive, from nurse to forager. They spend their first three weeks at home, repairing the nest and caring for their baby sisters. Let´s keep the analogy from the intro in mind. Instead of hands, nurse bees have brood glands with which they feed the larvae sugar infused pollen (“jelly”) – a food source high in proteins. Only nurse bees have brood glands and an abdominal fat body for the storage of proteins and lipids.
But just like in our intro the brood glands (hands) don´t stay with them forever. They lose these physiological characteristics in week four by transforming into foragers and go on their first foraging flight. During this foraging flight the levels of a certain neurotransmitter, octopamine, greatly increase. This is no coincidence! It´s been shown multiple times (by force-feeding the poor bees with octopamine) that this neurotransmitter can send 4 day old bees into a premature foraging frenzy. It´s as if it was possible to inject a hormone into a 4 year old toddler and suddenly the kid insisted on filling out the annual tax form for you – and did it better than you! (Unless you are Uli Hoeneß, that is.) Octopamine regulates the physiological change depending on age and social role that´s needed in the hive by binding to two different kinds of receptors in different brain regions- a Ca2+ linked receptor (age related change) in the antennal lobe and a cAMP – coupled receptor (social role change) in the mushroom body.
The mushroom bodymushroom body, which I have studied excessively in the fruit fly, is essential for learning and the formation of memories in insects and needs to develop the most for the transition from nurse to forager. Without proper capacities to learn and store memories, the bees would never find their way back from the flowers to the hive.
The development of the mushroom body (it really looks more like two intertwined cobras lifting their heads up if you ask me, but I must admit “Intertwined Cobras Lifting Their Heads – Body” is a bit of a mouthful) is also influenced by the juvenile hormone. Contrary to the implication if its name, the juvenile hormone doesn´t keep the bees looking young and juvenile. Instead, it accelerates growth. Its antagonist is the hormone vitellogenin, which has been named the key to anti-aging. The drugs industry doesn´t seem to have caught on yet, but in bees this hormone works like a charm. Normally, once bees start foraging, they live 7 – 10 more days and then die. If there´s a lack of nurses, octopamine reverses the forager status and the high levels of vitellogenin increase life expectancy by nearly 40%. Winter bees, which develop when there is no brood and therefore no foraging necessary, have the highest vitellogenin levels after the queen bee and can live up to 240 days (!) instead of the 7 days a forager has left. In human terms: If 4 weeks is the normal lifespan of a bee and a human has approx. 65 years to live, then this would mean a human would suddenly, through the expression of a single hormone, grow as old as 550 years! Excuse me while I run off to the patent office. But why do bees stop producing vitellogenin as soon as they go from nursing to foraging? A number of theories have been flung out there and, to my mind, the most appealing one is the following: Vitellogenin is involved in the immune system. Once the levels of vitellogenin drop, so does immunity. This means foragers, the bees that leave the hive, explore the world and get exposed to all sorts of nasty pathogens, are also the ones most susceptible to succumbing to said pathogens. This makes a lot more sense if you think about it this way: a bee that has been infected by a virus and promptly dies of it can´t carry it back to the hive to infect its sister bees. The short life span of a forager is another tribute to the grand eusocial scheme of social insect life.
In summary, sociality is a tough subject. Scientists are able to say which neurotransmitters are responsible and even which receptors in which brain compartments contribute to the proper division of labor. But the exact biochemical pathways are still a mystery. Do vitellogenin and the juvenile hormone interact directly to enforce the transition from nurse to forager? And if octopamine can reverse this change, does it influence the exact same pathways as these two hormones do? Are other receptors besides the ones mentioned here at play? Can I simply inject vitellogenin into my blood and live forever? (The latter would require a terrible method of vitellogenin extraction, which leaves Elizabeth Bathordy, “The Blood Countess” from 17th century Romania looking like a saint: To collect insect hemolymph (the insect blood analogue) in the lab, animals get their limb partly cut off and then spun at a comfy 13.000 rotations per minute. Needless to say, they don´t survive the procedure.) Research has only gotten started on deciphering the neurochemical code of social insect programming.
So, what have we learned during these three bee weeks? 100 million years ago in the Mid – Cretaceous, the first wasp accidentally fed pollen to its larvae. This was the beginning of pollenivory as we most commonly know it and simultaneously set off the co- evolution of flowers and bees. Bill Hamilton introduced sociobiology to the world and Richard Dawkins wrote a book about it. Kin selection theory, with its elegant c<rb equation, explains altruistic behavior by stating that higher levels of relatedness are served in order to keep the selfish gene alive. Bees are haplodiploid, with haploid males which are born from unfertilized eggs and have only one chromosome set, and diploid females born with two chromosomes from fertilized eggs. Drones (male bees) ejaculate with such explosive force that their penis ruptures and is left, along with some organs, inside the mounted queen bee, which flies off back into the nest, leaving a trail of dead lovers in her wake. I didn´t mention that before? How rude of me to keep that little nonsensical jewel of a fact from you! There is so much more to learn about the bee than I was able to go into detail with in these three short blog posts. But I hope you were able to understand the extraordinary biochemical drive of eusocialty and even more importantly enjoy the Three Bee Weeks while they lasted. So keep those brains buzzing! It´s what they like to do.
As for myself personally, I also learned a lot these three weeks, most importantly:
Never to make promises about publication dates.
Division of labour in honey bees: age- and task-related changes in the expression of octopamine receptor genes, Reim, T. and Scheiner, R.